Abstract
In this work, scanning electron microscopy (SEM), X-ray diffraction (XRD), and infrared spectroscopy (FTIR) techniques were used to study blue, red, and ochre pigments from wall paintings of the 16th century colonial convent of San Nicolás de Tolentino in Actopan, Hidalgo, Mexico. In the blue pigments, nanometric fibers with a chemical composition of mostly O, Si, Al, and Mg were identified. XRD and FTIR analysis indicated the presence of palygorskite clay, which suggests that these analyzed blue pigments are similar to Mayan blue. In the red pigment, structures with different morphologies (spines and flake shapes, for instance), with a composition of C, O, Al, Si, S, Ca, Na, Mg, and K and a higher concentration of Fe and Pb, were observed. Complementary analysis showed that the red color originates from hematite and lead. Finally, the ochre pigment showed a significant presence of O and Fe, which was associated with the goethite mineral, while calcite was a crystalline phase identified in all analyzed pigments; these show that these pigments are characteristic of the known Mexican Colonial color palette.
Highlights
From prehistoric times, people have sought to represent and transmit beliefs, culture, religion, and what happened in the environment, preserving what is beneficial and essential for survival and well-being [1,2]
In the scanning electron microscopy (SEM) micrographs, nanometric fibers in the blue pigments were observed; from the average diameter and chemical elemental composition, they can be associated with the palygorskite and sepiolite clays [51]. This assertion was supported by the X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) results, which effectively showed the presence of both clays, with palygorskite being the most abundant, and this was confirmed by EDS analysis finding elements such as O, Si, Al, and Mg
The greater amount of Ca is associated with calcium carbonate, which was the substratum in which the wall paintings were made, and the rest is related to calcium sulfate reported in blue, red, and ochre pigments. This assertion was supported by the XRD and FTIR results, and it should be mentioned that, since 1933–1934, colonial convents were under the protection of the INAH (Instituto Nacional de Antropología e Historia), and a layer of plaster was placed on the wall containing the paintings in order to preserve them
Summary
People have sought to represent and transmit beliefs, culture, religion, and what happened in the environment, preserving what is beneficial and essential for survival and well-being [1,2] In this respect, mural painting has played an important role in the history of Mexico because through it, we can learn many facts regarding pre-Hispanic life, the development of the Spanish conquest and colonization, and the independence and the modern life of Mexico. The raw materials used to elaborate these earlier paintings had a regional origin and were categorized as organic, inorganic, and synthetic [7]; The earlier mural paintings were made by the fresco technique by anonymous artists with careful monitoring by the monks. The second were mainly manufactured from minerals such as iron oxide, yellowcochineal
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